Planographic printing surface



My 27,"'1'9'30. I R. F. REED Fl AL 1,759,956

PLANOGRAPHIC PRINTING SURFACE Filed Jan. 19, 1929 V llll Ink receptive surface Water receptive surface I v 3 2 3 v Patented May 27, 1930 application Serial No. 257,553, filed Febru- UNITED STA res PATENT OFFICE 3.03am: I. REED, or NORWOODQAND ram. w. DORST, or CINCINNATI, omo, AssIen' one mo THE m'rnoemrmc TECHNICAL FOUNDATION, me, on NEW Yonx; N. Y.,

A CORPORATION 01' DELAWARE PLANOGRAPHIG PRINTING S U RFACE Application filed January 19, 1929 Serial No. 833,739.

This application is a continuation of our ary 27, 1928, for planographic printing surface. This invention relates to a novel planographic printing surface and to a new process of-preparing the water-receptive, non-printing areas of planographic printing surfaces. he printing surfaces embraced within the scope of this invention are those adapted for use on the various types of lithographic and 'oflfset presses, these surfaces in general being characterized by the fact that certain portions, called the image or design, are receptive to grease, lithographic ink, etc., and repellent to water, and that the remaining portions are receptive to water and repellent to grease, lithographic ink, etc. when they are moistened with water. It has been the practice in the past to form the grease-attractive image or design on a supporting material such as a lithographic stone, metallic plates, or on celluloid by any one of a number of methods; for example:

(1) Writing or drawing directly on the stone or metal with a greasy ink, tusche, or crayon.

(2) Transferring a greasy design to the surface of stone or metal by methods known to the art.

(3) Coating the surface of stone or metal with a sensitized colloid and ex osing it to light in contact with a negative 0 the design, or by projection, thereby forming a positive print on the surface, composed of insoluble colloid which is rendered grease-attractive for the urpose of printing.

(4) oatmg the surface of stone or metal with a sensitized colloid and exposing to light in contact with a positive transparency of the design, therebyforming a negative print on the surface, composed of insoluble colloid; removing the soluble colloid from the areas protected against lightexposure by the positive transparency, and replacing it with a greasy material,the light-hardened colloid actin as a stencil which is afterwards remove leaving the'greasy printing image.

Regardless of the method employed to produce the greasy printing image or design,

the remaining (portions of the surface which are not desire to print have, in the past, been rendered water-receptive and greaserepellent by treatment with aso-called etch or desensitizer composed of an acid, salt, or mixture of both, either alone or in combination with a solution ofgum arabic. This so-called etching operation is invariably followed by an ap lication of gum arabic solution whlch is su sequently dried.

The present invention consists of improvements in methods of treating the non-printing areas of planographic printing plates to render them water-attractive and grease-repellent.

According to this invention the support-- ing' material may be lithographic stone, zinc, aluminum, celluloid, rubber, or any material having the necessary mechanical properties and, preferably a surface grain or a porous structure. This invention comprises the formation of a durable hydrophili'c film on the portions of the surface of such a supporting material which are desired not'to print. The greasy printing image or design may be produced by any method known to the art.

The object of the invention is to produce non-printing areas on a planographic surface which bound the greasy printing image or design, which non-printing areas are waterreceptive, and in addition are durable and resistant to abrasion, oxidation, and other actions which usually destroy the grease resistance of said non-printing areas produced by previous" methods, and thus necessitate frequent etching and gumming of the surface during the' rinting operation.

Another 0 ject is to produce a planographic printing surface, the properties of which are It must be understood that these views are both diagrammatic enlargements intending to show the general nature of the invent-ion and the relative disposition of the materials used and are not intended to represent proportions and relative thicknesses with accuracy since the thinness of the actual films involved and the imgossibility of measuring them accurately ren ers scale drawings impossible.

As disclosed, a support 1, preferably meetching liquids. Moreover, the water-receptive surface is so absorbent to water that it permits the plates to be wet by a liquid devoid of etching acid so that this water-receptive film not only protects the ink-receptive surfaces, but obviates the use of a conventional etching material which is injurious to the inkrecept1ve surfaces.

While the above description is directed to the'use' of the preferred films, that is, light hardened albumen and light hardened gum arabic, the above disclosure must be read in relation to the remainder of the specification which more fully develops and explains the invention. 7

According to prior art, certain colloids, e. g. gelatin, glue, albumen, casein, etc., when mixed with chromic acid or a salt thereof become sensitive to light. When such a mixture is coated on a stone or metal surface and exposed to the action-of light, it is rendered insoluble in water and caused to become greaseor ink-receptive in proportion as it. becomes insoluble. This knowledge has been made use of in the various methods of photoetching, photo-lithography and collotype.

Now what has not been known to prior art is that certain colloids, when properly sensitized and exposed to light, become physically stable, strong gels long before they attain the slightest grease-receptive properties. Such gel films when produced properly on planographic printing surfaces are water-receptive and grease-resistantto a high degree, and, in addition, possess great strength, durability, and resistance to abrasion and the action of dilute acids and alkalies. When produced on the non-printing areas of a planographic printing plate, they constitute a surface greatly superior to the surface produced by known methods of etching or desensitiz- 1ng said surface to grease. These hardened COllOld films, because of their great strength and appreciable thickness, rotect the grained surfaceof the planograp iic printing plate loid.

- 3. Intensity of light to which it is exposed.

4. T1me of exposure. 5. Thickness of the film.

6. Reflecting power of the material constituting the support.

7. Nature of the surface grain of the support.

Numerous colloidal substances are susceptible of use in forming such hydrophilic films.

These include gum arabic, dextrine, modified starch, agar-agar, etc. For the purpose of disclosure, gum arabic is chosen, as it typifies the class of substances which can be made sensitive to the action of light by admixture with chromic acid or a salt thereof, and used to produce the desired results.

The planographic printing surface produced according to this specification differs from collotype and photo-gelatine printing surfaces in that the non-printing areas are produced by means of separate materials and in a separate and distinct operation from that used in preparing the image or design areas, whereas in the collotype process, both'the design and non-design areas are composed of the same material, namely, gelatine, the desi portions being formed by sensitization of the whole surface and selective exposure of the desired areas to light- In our process the image and non-image areas therefore are each composed of the most favorable materials, treated individually to produce the particular optimum conditions for durability and service of each area, whereas the weakness of the collotype and similar processes lies in the fact that no single colloid coating can be made to assume maximum ink preferring powers in one area, maximum water preferring powers in another area, and maximum durability of both areas at the same time.

As an example of the method used which yields satisfactory results, the following procedure will serve:

A solution composed of 1 part ammonium bichromate, 15 parts air dried gum arabic, 45 parts water, is coated on a grained planographic surface on which a greasy or grease- 2. Proportion of sensitizing agent to colreceptive image or desig:l has been produced by any of the methods own to the art. A

grained surface is desirable because all films adhere to it much better than to a polished surface. For the purpose of this disclosure it makes no difference whether or not said surface has previously received the conventional lithographic etch, since the described treatment alone produces the improved ink-repellent surface. The coating operation is not limited to anyone method, but includes coating by hand as in the well known operation of gumming up, coating on a whirler,

brushing, flowing, spraying, or dipping. Af-

ter coating the surface, the coatlng is dried and exposed to the rays of an are light or any other light source of suflicient intemsity."

the same total light energy is furnished to a unit area of the coating.

After exposure, the surface is thoroughly washed to remove unchanged ammonium bichromate. The surface may or may not be gummed in the conventional manner before proceeding with the printing operation, but

gumming is recommended, as it makes possible greater hardening of the colloid without danger'of it becoming grease-receptive than is the case if gumming is omitted.

L This invention is not limited by this example, since a wide range of compositions of the colloid mixture may be used and a similar result obtained by properly adjusting the degree of exposure. For example, a solution containing the proportion of one part of ammonium bichromate to five parts of air dried gum arabic, coated and dried on an aluminum surface and exposed under the above described conditions for thirty seconds will produce a suitable hydrophilic film. A solution containing the proportion of one part of ammonium bichromate to thirty parts of gum arabic, coated on a similar surface, dried, and exposed under the same conditions for six minutes will also yield a suitable hydrophilic film. The latter proportion constitutes approximately the practical lower limit of bichromate concentration, since a proportion of less than 1-30 requires an exposure of impractical length and even then does not yield the best results. The upper limit of bichromate concentration is approximately the proportion at which the bichromate crystallizes visibly when the coating is dried before exposure. This description refers particularly to ammonium bichromate but chromic acid or any of itssalts may be substituted with certain modifications. In like manner the light exposure to be given a coatin selected composition may be varied certain limits and still produce the desired results but to a diminishing degree as the conditions vary from the optimum. An exposurev of ten minutes or more is required to produce definite grease-receptive properties in a coating of the composition, and under the exposure conditions specified in above example.

The reflecting power of the support is a factor iii determining the amount of exposure to be given in any case. The coating of any on azinc surface requires a somewhat longer exposure than on aluminum.- On a white opaque celluloid or pyroxylin surface the exposure should be shorter than in the case of aluminum.

The advantages gained by the above described invention are listed as follows:

1. The hydrophilic film produced is of appreciable thickness and is capableof imbibing and holding moisture. It therefore does not dry out as quickly as water-attractive surfaces produced by previous methods.

2. Since the hydrophilic film produced is relatively hard and resistantto abrasion, it practically eliminates the chemical nature of the solid support from the field of action.

Any solidmaterial of suitable mechanical properties may therefore be used as the support or printing plate. The hydrophilic fihn prevents wearing away of the grain of the supporting material.

3. Since said hydrophilic film prevents grease adhering permanently to the surface, little or no corrosive material need be used in the dampening solution during printing, with the result that the printing areas are not undermined and do not work sharp or diminish in size.

4. Said hydrophilic film protects metal printing surfaces from the oxidizing action of water and oxygen under ordinary printing conditions.

5. The hydrophilic film prepared by the proposed methods is of appreciable thickness, being of approximately the same magnitude as the thickness of the photo-lithographic printing image. This image therefore does not stand up in relief from the lithographic surface as in the previous process and is therecessive abrasion. In either case, the life of the printing image is greatly prolonged.

6. The high lights of the design to be printed lithographically are kept absolutely clean with less surface moisture than is required on surfaces produced by previous methods of etching. This .is true even of the finest lights occurring in the shadows of a half tone or grained screen image, with the result that detail is preserved indefinitely, which formerly was lost after a few impressions.

7. The hypdrophilic surface coating will stand much abuse, such. as drying, abrasion, and treatment-with chemicals, soap, solvents, oils, greases, inks, and asphaltum without additional protection, which would ruin planographic surfaces prepared by ordinary methods:

8. The proposed methods make possible the use of finer grains than are now possible. Finer grains make possiblesmoother, denser solids and the use of finer screens.

9. In case of damage to the hydrophilic surface film through accidents during printing or through excessive abrasion occurring 1 during long editions, said hydrophilic film The use of softer inks reduces the can easily be renewed while the plate is on the press by coating with-the colloid mixture and hardening by proper light exposure.

10. Since less moisture is required to keep the non-printing areas of planographic surface ink-repellent, the ink impressions on the material being printed are brighter and more dense than ink impressions from plates prepared by previous methods.

'11. The so-called processes of-dry-lithography, in which inks containing a watery liquid or a deliquescent substance are printed without a separate dampening operation, are facilitated.

12. Both proving and machine printing can be done more rapidly and with less labor than heretofore. 1

13. Chromic acid etches with their recognized evils can be eliminated from the operations of transferring and printing.

14. Inks can be run softer, without danger of greasing or scumming), than on pianographic plates prepared y previous methods. This means smoother printing and better lifting of inks, especially yellows. It also means less abrasion and wear of the design, since softer inks are better lubricants. ull on the grippers, the danger of paper stic ing to the said remaining areas water-receptive.

2. The process of making a planographic printing surface,.which comprises the ste of coat ng a supporting surface with a colloidal material adapted to become ink-attractivewhen hardened to the point of physical stability, the step of so hardening a portion of said material to constitute an image, the step of removing the remainder of said material not hardened, the step of coating the portions of the plate other than the image with a colloidal material adapted to be water-receptive when hardened to the point of physical stability, and the step of so hardening said material.

3. A lithographic plate, the surface of which comprises printing and non-printing portions, the former, a grease-receptive film of hardened albumen, and the latter a'hydrophilic film of hardened gum arabic.

4. The process of making a lithographic printing plate, comprising, depositing a greaserreceptive printm upon said plate, andhardening a m of gum arabic over the remainder of said plate to provide the water-receptive nonrinting areas. 7

5. The process of ma ing a lithographic printing plate, comprising, depositing a grease-receptive printing film upon said plate to constitute the printing design, depositing a greasy ink upon said printing film, and hardening a film of sensitized gum arabic over the remainder of said plate to provide the water-receptive non-printing areas.

6.. In the process of making a planographic printing plate, the step of producing an inkreceptive design on a support, the step of depositing a greasy ink upon said design, the

step of coating the non-design portions of the plate with a light sensitive colloid, the step of exposing the resultant coat-ing to lightto a degree suflicient to cause said coating to become insoluble in water, but insuflicient to cause it to become grease-receptive when wet with water.

7. A lithographic plate, comprising, a supv 4, 120" port, and two organic colloidal films disposed side by side upon and adhering to said support, one of 'said films comprising a grease-receptive film, the other of said films eing a hydrophilic film of hardened gum arabic of sufficient thickness to afford protection to the grease-receptive film.

8. The process of making a planographic printing surface, which comprises, depositin an ink-receptive image upon a support, and hardening a film of organic hydrophilic material over the remaining areas of said support, said film of thickness suflicient to afior protection to the ink-receptive film.

9. A lithographic plate, comprising, a support upon which are disposed side by side two films of organic colloidal material adapt@ to adhere to said support, one of said films comprising grease-receptive light hardened albumen, the other of said films comprising water-receptive light hardened gum arabic said latter film of sufiicient thickness to afford protection to said first film.

10. A metal lithographic plate adapted to be used without an etching dampening liquid, said plate, comprising, a metallic support, and two colloidal films deposited side by side upon said plate, said films adhering to said support directly, one of said films being grease-receptive, the other of said films being water-receptive and sufficiently thick to protect the grease-receptive film and highly absorbent to water.

In witness whereof, we hereunto subscribe our names.

J ROBERT F. REED. PAUL W. DORST. 

